DMF is a commodity in the chemical industry, widely used as a solvent and as a reaction medium in the preparation of dyes.
One method for preparing DMF on a commercial scale is that in which DMA and carbon monoxide are catalytically reacted, using an alkali metal methylate as the catalyst. This produces crude DMF, which must be refined to be commercially acceptable. Before this is done, it is customary to remove the catalyst because its presence in the refining train together with water causes decomposition of the DMF product into DMA and formic acid, for obvious reasons an undesirable thing.
This removal is ordinarily done by adding water to the reaction mass just before it is fed to the refining train. This converts the catalyst to an alkali metal formate precipitate, as shown by the following equations: ##STR1## where X is an alkali metal.
As can be seen from equation (2), this procedure exacts an economic penalty because some of the product DMF is consumed. This yield loss can amount to as much as 2%, by weight. What's more, once the catalyst is so removed, it is lost and cannot be reused, which is another expense. To this must be added the additional cost of physically removing the alkali metal formate precipitate from the reaction mass.
It has now been found that the catalyst removal step is not necessary and that the catalyst can be preserved, recycled and reused if an excess of at least 0.1%, by weight, over the stoichiometric amount of DMA is present in the reaction mass at all times.